OBJECTIVE: To evaluate the inter-observer agreement of radiological diagnosis of lower respiratory tract infections in children. METHODS: Chest X-rays from 60 children younger than 5 years of age were evaluated by three physicians: a pediatric radiologist (PR), a pediatric pulmonologist (PP) and an experienced emergency pediatrician (EP). All children had sought an emergency room due to acute respiratory infections with apparent lower respiratory tract involvement. Observers were blinded to the original diagnostic conclusions, but clinical and laboratory data from the initial medical evaluation were provided with each film. Variables were grouped into five categories: a) film quality; b) site of abnormality; c) radiological patterns; d) other radiographic images; e) diagnosis. Inter-observer agreement was assessed using Kappa statistics, accepting prevalence-bias-adjusted values (PABAK). RESULTS:Kappa values for each of the three observer pairs (RP vs. PP, RP vs. EP, and PP vs. PE) were 0.41, 0.43, and 0.39, respectively. The overall inter-observer agreement was moderate (0.41). Agreement on other variables was as follows: regular for "film quality" (0.30); moderate for "site of abnormality" (0.48); fair for "radiological patterns" (0.29); moderate for "other radiographic images" (0,43); and moderate for "diagnosis" (0.33). The overall intra-observer agreement was "moderate" (0.54), which is below the agreement values reported by other studies on chest X-ray variability. CONCLUSIONS: Inter-observer variability is an intrinsic characteristic of the interpretation of chest X-rays, and the diagnosis of lower respiratory tract infections in children remains a challenge. Most of our results were similar to those previously reported.